In an application wherein a solenoid-actuated valve is used to control the flow of a fluid (e.g., coolant, fuel vapor, exhaust gas, gasoline), it is frequently desirable to be able to monitor one or more parameters of the fluid. In some applications, fluid flow is the parameter which needs to be monitored, while in other applications fluid pressure or fluid temperature are parameters whose values need to be monitored. In any case, information concerning the measured parameter needs to be developed economically and reliably, and that information needs to be fed back to monitoring/control circuitry.
It is also desirable to be able to monitor the operation of the valve itself. If the solenoid which actuates the valve is shorted, open, or otherwise malfunctioning, that information also needs to be sent back to the monitoring/control circuitry.
In the past, testing and/or monitoring the operation of solenoid-actuated valves has typically required the use of additional electronic circuitry which can raise system costs to an unacceptable level. Further, the inclusion of such testing and/or monitoring circuitry has resulted in the use of additional electrical conductors to carry information between the monitored valve and the monitoring/control circuitry.